The cardiovascular response to submaximal exercise in a chronically instrumented trained dog is a decreased heart rate, increased contractility, and increased end-diastolic ventricular volume. These changes are associated with a coronary blood flow response that is the same as before training. During the training program, coronary blood flow was found to be reduced at the same workloads compared to the untrained condition. These results suggest a biphasic response in the coronary vascular bed to training which may be due to a neurogenic component. Removal of the left stellate ganglion resulted in a completely different response of the heart to training. Atrial pacing and coronary reactive hyperemia were used to demonstrate a potential increase in the coronary vascular bed size. The periments proposed will determine the myocardial oxygen consumption, substrate utilization, and coronary vascular responsiveness in the instrumented conscious dog during various stages of an exercise training program. The change in coronary flow during the early part of the training program will be maintained by modifying the training program. At the termination of the training program, the ability to modify detraining in terms of heart rate and coronary blood flow will be investigated. The changes in coronary flow with training will be correlated with the changes in the determinants of myocardial oxygen consumption and also with substrate utilization of the myocardium. The role of the left stellate ganglion in the cardiac response to exercise training will be investigated further by performing a spinal dorsal root section from C8-T5. This will remove the major portion of the sympathetic afferent fibers that send information to the central nervous system. This study will be used to separate the efferent and afferent fibers in the left stellate ganglion and their role in the training response. These studies will furnish basic information about the mechanism(s) underlying the change in the coronary vascular bed and their significance with training and detraining. The role of the autonomic nervous system will be further investigated.